Having had many hours experience mowing with a front-mower on a skid-steer (and I like 'em a lot), me thinks that your distance concern may be overstated. For 150 acres, a bigger machine will surely be cheaper. Unless, of course, you have nothing else to do and don't care if the project takes you a very, very long time.
Or. . . if it's "sage brush, a little lighter", what about a heavy duty batwing cutter, such as a Woods BW 1800 or BW2400X behind an ag tractor? The higher-end Woods batwings have a deeper deck than many others, accomodating more cut material. With these you can drive slowly but get done fast. I have a lighter, BW180, and was surprised to find that I can trim with it around terrain and obstacles that I can't with smaller mowers--the overlap (extension beyond your tracks) allows you to trim up to or over obstacles and ditches. If you try this, I strongly recommend that you use a tractor rigged with (3) hydr actuators, so that you can control the height as well as both wings individually. Otherwise, if you T the two wing lift cylinders together, whichever one has the least pressure on it will raise all the way up before the other one begins to lift--like my hay tedder.
If you are going to own the 150 acres and maintain it, the batwing will be a great asset to own. I like my other stuff but looking back, I wish I had bought the batwing first . Mow everything you can with that first, then worry about the problem spots.